The ability to recognize social and moral norms, and use them to guide behavior, is fundamental to social cohesion and harmony. One prominent norm that guides adults' and children's actions and evaluations of events is the norm of a fair distribution of goods based on the principle of equality: that, all other things considered, good should be divided equally to recipients. The goal of the proposed experiments is to test a new developmental model regarding the development of fairness sensitivity within infancy, that stresses infants' interactions with caregivers in the context of sharing games as the source of age-related changes and individual differences in infants' acquisition of equality norms. The proposed research has 3 specific aims, 1) to characterize the development origins and trajectory of infants' burgeoning acquisition of equality norms, 2) to investigate the causal role f sharing experience infants' responses to inequality, 3) to investigate the nature of infants' responses to inequality, and, more specifically, whether and when such responses become moral intuitions. We test 3 central hypotheses regarding infants' developing sensitivity to fairness in the context of resource distribution tasks. The first hypothesis is that developmental changes occur between 6 and 9 months of age in infants' ability to detect inequality, coincident with the onset of sharing experience. The second hypothesis is that individual differences in infants' inequality responses arise from individual differences in parental dispositional empathy that influence the ways in which parents emphasize principles of equality and reciprocity in infant-caregiver interactions. The third hypothesis is that infants' inequality responses incrementally, and over time, begin to encompass various affective and cognitive components of more mature moral judgments. Across 10 experiments 6 to 24-month-old infants take part in both implicit tasks (based on looking times and pupil dilation) and explicit tasks (based on infants' overt social behavior) to investigate developmental changes and individual differences in responses to inequality. The proposed experiments are conceptually innovative because they 1) test a novel theoretical model with respect to infants' burgeoning fairness concerns that stresses the role of both parental attitudes and everyday experience in early social cognition, 2) seek to establish criteria for investigating the origins of moral judgment in infancy, and 3) investigate the origins of individual differences in early social cognition. The proposed work is also methodologically innovative as it introduces 3 novel experimental tasks and a novel dependent measure (pupil dilation) to study infants' acquisition of socio-moral norms; the introduction of these methods will have broad- ranging effects on the field or early perceptual and cognitive development by increasing the armory of tools and techniques available to developmental scientists. Finally, the proposed work may have import in the diagnosis and remediation of developmental disorders, such as autism, that are characterized by social deficits, including a recognition and understanding of social norms.